In orthopedic surgery, total joint replacement (also called joint arthroplasty) is performed where indicated on patients suffering from diseased bone due to osteoarthritis. Prosthetic components replace the end of the bone and the corresponding socket of the articulating bone that together form, e.g., a hip or shoulder joint. In the more common case of hip arthroplasty, the femur, the ball of the hip (head of the femur) and the cup of the hip (acetabulum) are replaced by endoprosthetic implants. Hip implants typically comprise two main components. The femoral component is anchored within the existing femur and includes a head that replaces the natural head of the femur. The acetabular component is secured within the acetabulum of the patient and serves as a bearing surface for the femoral component.
Most acetabular components include an outer shell or cup module and an internal liner, both of which have a semi-hemispherical shape. The outer shell has an outer dimension configured to fit and be fixed within the acetabulum of the patient. The outer shell is typically formed from a high strength metal such as stainless steel or titanium, in order to withstand the biomechanical forces exerted on the hip joint during normal activities. The inner liner is designed to be seated inside the outer shell by a locking ring or other retainer structure so that the liner locks within the shell. The inner liner is typically constructed of a polymeric material such a polyethylene. The liner serves much the same function as cartilage does in a healthy hip—it prevents the metal parts of the prosthetic joint from rubbing against each other.
The acetabulum is reamed and the proper outer shell size is determined by the surgeon. An example of a reaming system is disclosed in U.S. Pat. No. 5,658,290, including a surgical driver connecting with a domed cutting tool via catches that receive a pair of orthogonal bars from the tool. The tool presents an array of cutting teeth to form the hemispherical bone cavity of the acetabulum when rotated by the driver. The outer shell is positioned, aligned and then press fit into the reamed cavity, typically with the aid of an impact tool. The outer shell can be secured such as by screws which are inserted through a cluster of screw holes provided in the lower portion of the shell. Screw placement generally occurs in the posterior superior and/or posterior inferior quadrants of the acetabulum. The shell may be otherwise retained in the acetabulum, as will be appreciated by those skilled in the art.
At this point, the inner liner needs to be inserted into the outer shell. Before the liner is installed, there can be abnormal projections of bone (also known as “osteophytes”) usually caused by increased stress or wear on the ends of bones, as well as soft tissue, which protrude over the peripheral rim of the outer shell and interfere with the immediate placement of the liner. Traditionally, these protrusions have been cleared away by use of an osteotome (a chisel-like instrument) and a rongeur in a manner which is not optimally efficient. When the osteophytes and soft tissue have finally been cleared from the outer shell periphery, liner placement may proceed using the locking ring inside the outer shell. The hip replacement procedure is then finished by securing the femoral component as is well known.
It is desirable to provide a surgical tool, instrument and kit allowing timelier, more efficient removal of excess bone and soft tissue from the periphery of the implanted outer shell, which improves placement of the inner liner during total hip replacement.
It is further desirable to provide surgical tools, instruments and kits, which function with existing prosthetic components and implantation systems.
Accordingly, there is a need to provide an improved means for osteophyte removal that further functions with existing rotary power drivers to track the shape of implantable components in the body of a patient without the risk of over-cutting. Particularly, there is a need for visual confirmation by the surgeon of the position of the tool as the osteophytes and excess soft tissue are being fully sheared.
There is a further need for a rotary cutting tool having a tooth design that precisely shears osteophytes and soft tissue along the desired periphery of an implantable cup received in the bone cavity, while employing a linear cut guided by accurate visual confirmation by the surgeon.